1-but if you used %work complete it would mean the same thing correct?

Yes. However, it is a best practice to confirm remaining work. If you just update % work complete, Project will assume your original estimates was accurate. Ask for actual and remaining work and Project will calculate % work complete.

2-also per your answer i inserted actual work and remaining work columns into my gantt chart. but they both showed 0 for everything.

Project requires you to update tasks -- it does not update anything automatically.

and then strangely, when i updated just one of the tasks actual work, then the actual remaining updated only for that one,

Yes. If you update Actual Work, Project calculates Remaining work based upon Work - Actual = Remaining. It updates only the selected task.


and even if i brought that tasks actual work to 0 again, this time only for that activity the remaining work showed the actual remaining hours, not 0 like for everything else.

Actual work remains unless you manually delete it.

why did this happen? note: all these activities are in the future.
See above. The fact that tasks are in the future or the past doesn't mean anything to Project. It does not update anything automatically.

3-assume that later during the job, as the days progress and say for one activity there is little progress than planned. right now if you update the actual work and remaining work, % work and % complete columns calculate update the same. but if there was a delay they would not calculate the same correct?

If resources are working less hours per day than planned, I would update that data in either the Task Usage or Resource Usage view. Add Actual work to the right side and enter the work per day or week. If you just update from the Tracking Table -- Project assumes the work was done as scheduled.